Inorganic materials such as metals and ceramics excel in heat resistance, mechanical strength, electrical properties, optical properties and chemical stability, which make them widely applicable in industry. However, they are generally brittle and high in hardness. Accordingly, they must be processed or machined at high temperature in order to impart desired shapes thereto. This sometimes limits their uses.
On the other hand, organic polymers are superior in moldability and flexible, which make them well processable. However, they are mostly inferior in heat resistance and chemical stability to inorganic materials. This has led to recent extensive development of organic polymers using metal alkoxides as starting material, called organic-inorganic hybrid materials or organic-inorganic nanocomposites.
Application of such organic-inorganic hybrid materials to optical waveguides is contemplated in Patent Literatures 1 and 2.
However, in either case, a so-called sol-gel process is utilized in which a metal alkoxide is used as a starting material and water is optionally added to effect a hydrolysis reaction. As a result, a large amount of water (H2O) or silanol groups (Si—OH) is left in materials. In particular, silanol groups are hard to remove as by heating and accordingly become a main cause of optical loss primarily in the infrared region. In particular, their influence becomes significant in the region around 1500 nm which overlaps a wavelength band for optical communication.
Patent Literature 1: Japanese Patent Kokai No. 2000-356722
Patent Literature 2: Japanese Patent Kohyo No. 2001-506372
Patent Literature 3: Japanese Patent Kokai No. Hei 6-322136
Patent Literature 4: Japanese Patent Kokai No. 2003-195070
Patent Literature 5: Japanese Patent Kokai No. 2000-336281
Patent Literature 6: Japanese Patent Kokai No. 2000-34413